Process for the preparation of enol esters of straight chain carboxylic acids

ABSTRACT

Methylacetylene and allene are equilibrated by contact with potassium hydroxide in an inert solvent such as t-butanol. When mixtures of methylacetylene and allene are used in a chemical reaction such as the preparation of isopropenyl stearate from stearic acid and zinc stearate is the sole catalyst, methyl acetylene is selectively absorbed by the stearic acid leaving behind highly purified allene. Alternatively, when potassium stearate is present with the zinc stearate and sufficient stearic acid is present, the allene-methylacetylene mixture is completely absorbed. The zinc stearate-potassium stearate co-function synergistically.

United States Patent [191 Rothman et al.

[451 Apr. 15, 1975 Samuel Serota, Philadelphia, both of Pa.

[73] Assignee: The United States of America as represented by theSecretary of Agriculture, Washington, DC.

22 Filed: Dec. 15, 1972 21 Appl. No.: 315,732

Related US. Application Data [62] Division of Ser. No. 176,735, Aug. 31,1971, Pat. No.

[52] US. Cl 260/410.9 N; 260/497 R; 260/498 [51] Int. Cl. C07c 67/04[58] Field of Search 260/410.9 N, 498, 497 R [56] References CitedUNITED STATES PATENTS 3,655,736 4/1972 Norton et al 260/497 R PrimaryExaminer-Alton D. Rollins Assistant Examiner-+ Diana G. Rivers Attorney,Agent, or FirmM. Howard Silverstein; Max D. Hensley; William E. Scott[57] ABSTRACT Methylacetylene and allene are equilibrated by contactwith potassium hydroxide in an inert solvent such as t-butanol. Whenmixtures of methylacetylene and allene are used in a chemical reactionsuch as the preparation of isopropenyl stearate from stearic acid andzinc stearate is the sole catalyst, methyl acetylene is selectivelyabsorbed by the stearic acid leaving behind highly purified allene.Alternatively, when potassium stearate is present with the zinc stearateand sufficient stearic acid is present, the allenemethylacetylenemixture is completely absorbed. The zinc stearate-potassium stearateco-function synergistically.

3 Claims, No Drawings PROCESS FOR THE PREPARATION OF ENOL ESTERS 01FSTRAIGHT CHAIN CARBOXYLIC ACIDS This is a division of application Ser.No. 176,735, filed Aug. 31, 1971, now U.S. Pat. No. 3,745,195.

A non-exclusive, irrevocable, royalty-free license in the inventionherein described, throughout the world for all purposes of the UnitedStates Government. with the power to grant sublicenses for suchpurposes, is hereby granted to the Government of the United States ofAmerica.

Processes for the equilibration of allenemethylacetylene mixturestypically involving a gasphase, thermally facilitated operation using acatalyst of alumina or silica activated by a variety of halogens orhalogenated hydrocarbons are well known in the art (U.S. Pat. Nos.3,268,614, 2,594,706 and 3,243,470 and French Patents 1,370,415 and1,370,416). With one exception, U.S. Pat. No. 3,268,614, none of theseclosely similar procedures attempt the difficult separation of pureallene from such mixtures. The difficulties of separation arise not onlybecause the boiling points of allene and methylacetylene are very closebut also because they distill together in an azeotropic constant boilingmixture. The exception referred to above involves selective complexformation with copper halide and is too costly for commercialapplication.

In previous studies concerning the addition of stearic acid tomethylacetylene to form the enol stearate, isopropenyl stearate(co-pending appl. Ser. No. 822,693, filed May 7, 1969, now U.S. Pat. No.3,666,781), we were hampered by the problem that cheap, commerciallyavailable weldingtorch gases containing mixtures of allene andmethylacetylene in about equal proportions were useful only for themethylacetylene content. The recycling of the allene was expensive sinceequilibration by known procedures gave only a fixed proportion ofmethylacetylene requiring an infinite geometric series for completeutilization.

An object of the present invention is to show that the known type ofequilibration can be achieved much more simply than previously possibleby using as catalyst potassium hydroxide in t-butanol or similar inertsemi-solvent.

In general, according to this invention we have found that when bothcomponents of the equilibrium are used in a given chemical reaction suchas the formation of isopropenyl stearate from stearic acid, it ispossible to isomerize simultaneously the allene to methylacetylene andabsorb this newly formed methylacetylene as rapidly as it is formed withstearic acid to form isopropenyl stearate. The continuously shiftingequilibration occurs until, provided sufficient stearic acid is present,all of the allene-methylacetylene mixture is consumed. In order toachieve complete consumption of the allenemethylacetylene mixture thecatalyst must be a mixture of zinc stearate and potassium stearate. Theunusual and unpredictable synergism between these two stearates is animportant facet of this invention because there is a total lack ofreaction between stearic acid and allene when either catalyst is usedalone. Furthermore, we have found that the selectivity of stearic acidfor methylacetylene to the exclusion of allene is so marked that allenemay be freed of any amount of methylacetylene provided that adequatestearic acid is present and that the catalyst be only zinc stearate.

So for, for the sake of simplicity, we have specified stearic acid.However acids from acetic to n-eicosanoic acid are suitable regardlessof whether unsaturation is present or whether the acids are in a mixturesuch as those obtained from hydrolysed tallow of vegetable oils. Thezinc stearate and potassium stearate can be conveniently prepared insitu by adding to an excess of melted stearic acid the calculated amountof zinc oxide and/or potassium hydroxide or similar basic salts capableof forming the required salts by neutralization.

We stated previously that the catalyst, potassium hydroxide, is in aninert solvent such as t-butanol. It is not strictly necessary that thesolvent dissolve all the potassium hydroxide or even that the solvent bepresent at all, but only that the solvent be inert. Solvents such asn-octadecanol and similar ones of lower molecular weight absorb bothallene and/or methylacetylene to form novel unsymmetrical isopropenylalkyl mixed ethers such as isopropenyl octadecyl ether m.p. 29.5-30C.Ethers such as diethyl ether, dioxane, and tetrahydrofuran are suitablesemi-solvents for the indicated isomerization.

The indicated reactions are typically carried out in pressure vessels at150C and 600 psi pressure at the indicated temperature for 4 to 20 hoursreaction time. Occasionally, even much shorter times suffice. Theexamples that follow will show the deviations allowable from theseconditions of time. temperature, and pressure without seriouslyaffecting the yield.

The utility of methylacetylene has been well documented for enol estersynthesis. Allene essentially free of methylacetylene is useful as astarting material in the preparation of propargyl alcohol anticorrosiveformulations and for polymer synthesis, for example. methyl methacrylateproduction and polymerized allene per EXAMPLE 1 t-Butanol, 250 ml. and27 g. of freshly powdered commercial reagent potassium hydroxide wereheated with slightly more than a mole of pure allene in an autoclavepressurized to 350 psi with nitrogen at room temperature and heated to150C for 14 hours. The maximum developed pressure was 560 psi. Infraredassay of the gases showed the typical equilibrium proportion of majoritycomponent methylacetylene and minority component allene.

EXAMPLE 2 Stearic acid, 282 g. (1 mole), and 30 g. of zinc stearate weremelted in an autoclave to a single phase and the vessel was sealed andwell purged with nitrogen. Propyne (methylacetylene) 16 g. (0.4 mole)and allene 16 g. (0.4 mole) were introduced via a pressure burette withnitrogen backup pressure, the vessel was heated to 150C, and pressurizedto 600 psi with additional nitrogen. After 14 hours, the condensablehead gases were verified by infrared analysis to be pure allene withonly a trace of propyne. (Allene shows strong bands at 5.15 and 5.9microns in the gas infrared ce11-regions of transparency for propyne;propyne bands at 4.7 microns were practically absent a region of allenetransparency thus enabling an accurate assay.)

EXAMPLE 3 A pressure vessel was charged with g. of stearic acid and 7 g.of potassium hydroxide with stirring until solution occurred. The vesselwas then purged with nitrogen and sealed. 0.75 mole of liquid pureallene was added via a pressure burette having a back nitrogen pressureof 340 psi. The vessel was heated to 150C for 12 hours and then cooled.Examination of the vessel contents showed only the presence of thestarting materials allene and stearic acid and catalyst; methylacetyleneand ester were absent.

EXAMPLE 4 A pressure vessel was charged with stearic acid. 282 g. (1mole), potassium hydroxide. 27 g. (0.5 mole approx), and zinc stearate.42 g. Heat was generated during the neutralization causing vigorousexpulsion of steam. The vessel was sealed and flushed with nitrogen andthen 0.24 moles of allene and 0.24 moles of methylacetylene were addedat 150C using a back pressure of 600 psi to force the hydrocarbons intothe vessel. After 17 hours. analysis of the head gas showed only tracesof hydrocarbon in the head space indicating total conversion toisopropenyl stearate. Isolation of isopropenyl stearate. 160 g..confirmed the analysis.

EXAMPLE 5 n-Octadecanol, 268 g. (1 mole), powdered potassium hydroxide,2.7 g. (.05 mole) and 1 mole of allene were heated to 150C for 24 hoursto yield the new compound n-octadecyl isopropenyl mixed ether. Theallene was totally consumed. The product was isolated by ex- EXAMPLE 6Results identical to those of example 5 were obtained using a mole ofpropyne instead of a mole of allene.

We claim:

1. A process for preparing enol esters of from 5 to 23 carbon atomscomprising reacting a member of the group consisting of saturated andunsaturated straight chain carboxylic acids having from 2 to 20 carbonatoms and mixtures of said carboxylic acids with a mixture ofmethylacetylene and allene in the presence of a catalyst consisting of amixture of zinc stearate and potassium stearate, said mixturecofunctioning synergistically and effecting a complete consumption ofsaid mixture of methylacetylene and allene and forming an isopropenylester.

2. The process of claim 1 wherein the enol ester is isopropenyl stearateand the member of the group is stearic acid.

3. The process of claim 2 wherein the reaction is conducted at about C.under 600 psi. pressure for about 17 hours.

1. A PROCESS FOR PREPARING ENOL ESTERS OF FROM 5 TO 23 CARBON ATOMSCOMPRISING REACTING A MEMBER OF THE GROUP CONSISTING OF SATURATED ANDUNSATURATED STRAIGHT CHAIN CARBOXYLIC ACIDS HAVING FROM 2 TO 20 CARBONATOMS AND MIXTURES OF SAID CARBOXYLIC ACIDS WITH A MIXTURE OFMETHYLACETYLENE AND ALLENE IN THE PRESENCE OF A CATALYST CONSISTING OF AMIIXTURE OF ZINC STEARATE AND POTASSIUM STEARATE, SAID MIXTURECONFUNCTIONING SYNERGISTICALLY AND EFFECTING A COMPLETE CONSUMPTION OFSAID MIXTURE OF METHYLACETYLENE AND ALLENE AND FORMING AN ISOPROPENYLESTER.
 2. The process of claim 1 wherein the enol ester is isopropenylstearate and the member of the group is stearic acid.
 3. The process ofclaim 2 wherein the reaction is conducted at about 150*C. under 600p.s.i. pressure for about 17 hours.